Recent advances in color ink-jet printer technology have made it possible to provide a high level of image definition for printed output of so-called photo-realistic image quality. In a color ink-jet printer capable of delivering such a high level of printout quality, color ink droplets are ejected to form dots of predetermined colors at desired points, thereby producing images in dot matrices. For color image printing, three primary color inks of cyan (C), magenta (M) and yellow (Y) or four color inks of cyan, magenta, yellow plus black (K) are used.
To realize photo-realistic quality, color reproducibility is of critical importance as well as fine dot formation. In the inside of a computer, colors are represented using red-green-blue (RGB) multi-level gradation data, whereas CMYK two-level gradation data is handled on a printer. Therefore, color space conversion and gradation conversion are performed for printout. Namely, in printing, CMYK two-level gradation is used while maintaining colors represented in RGB multi-level gradation on the premise that each dot is colored with specified density.
However, although color reproducibility is maintained with respect to print data on output, a volume per droplet of color ink may be different among print heads due to an instrumental error, resulting in each dot being colored with inconsistent density.
In the above-mentioned color ink-jet printer, if a volume per ink droplet ejected from its print head varies due to an instrumental error, each dot is not colored with specified density to cause a disadvantage of degradation in color reproducibility.
In order to circumvent this disadvantage, the inventors have examined an arrangement in which print data is adjusted in advance to compensate for an instrumental error and then a printing operation is performed according to the print data thus adjusted to improve color reproducibility. In this adjustment of print data, an adjustment table is used. For preparing an adjustment table, a patch pattern is printed in the entire gradation range using a reference print head which ejects each droplet of color ink in a specified reference volume, and also a patch pattern is printed in the entire gradation range using each print head having an instrumental error. Through comparison of patch patterns, error-free patch pattern combinations are determined, and thus a list of error-free patch pattern combinations, i.e., an adjustment table is created.
Although comparison of patch patterns is required, it is impracticable to compare patch patterns for all the colors to be reproduced. Therefore, the inventors have created an adjustment table for each element color. Although almost the same color reproducibility as with the reference print head has been attained in single-color printing, inconsistency has occurred in mixed-color printing.
In view of the foregoing, it is a principal object of the present invention to provide a print data adjusting system, a print data adjusting method, and a software storage medium containing a print data adjusting program for enabling accurate color reproduction regardless of an instrumental error among such parts as print heads.